This relates generally to displays, and, more particularly, to displays with external compensation for pixel variations.
Displays such as organic light-emitting diode displays may be used to display images for users of cellular telephones, watches, computers, and other electronic equipment. Each pixel in an organic light-emitting diode display may have an organic light-emitting diode that emits light in response to an applied current. A drive transistor and other pixel circuitry may be used to control the applied current and thereby adjust pixel brightness.
If care is not taken, pixel variations can adversely affect display performance. For example, some of the pixels in an organic light-emitting diode display may experience drive transistor threshold voltage shifts and light-emitting diode aging effects that can make those pixels weak. This can lead to undesirable variations in the image light output from different portions of a display.
Internal or external pixel compensation schemes can be used to help avoid non-uniform display output. With internal schemes, additional pixel circuitry is provided in the pixels to perform compensation. This pixel circuitry can consume significant area on a display and may therefore limit the maximum numbers of pixels per inch that can be included in the display. With external schemes, pixel measurement circuitry is placed in peripheral portions of a pixel array. These schemes allow pixel density to be enhanced, but may be insufficiently flexible to measure desired pixel attributes for compensation.